The so-called strobe effect is used in various fields, in which an observation target is observed in a stationary state or in a slowly moving slow motion state by emitting a flash light for a moment from a light source to irradiate the observation target in a periodic motion while repeating the emission of the flash light at a constant period. For example, as an observation target, in addition to a motor that rotates at a high speed in a constant period, a printer, a fuel ejecting device, etc., in which liquid droplets are ejected in a constant period and fly at a prescribed speed, can be exemplified.
By the way, as a method for observing an observation target that perform a periodic motion at a high speed, a method using the so-called high speed camera is known. In a high speed camera, an observation target is image-captured with more frames than a normal camera, and therefore the observation target can be observed in a stationary state or in a slowly moving state. However, since such a high-speed camera is expensive, it is difficult to feel free to observe the observation target in a periodic motion, causing an increased observation cost.
For this reason, various methods for observing an observation target in a periodic motion using a stroboscopic effect without using a high-speed camera have been conventionally proposed.
For example, Patent Document 1 discloses a light emission control device configured to move an observation/image-capturing target by shifting the light emission start time. The light emission control device not only moves an observation/image-capturing target to a prescribed position by shifting the light emission start time, but also move the observation/image-capture target for a long time covering a plurality of periods. With this, it is possible to continuously observe and image-capture a target 22 at a speed slower than the actual speed over a long period of time.
Further, Patent Document 2 discloses a droplet observation device in which a control means 6 generates a strobe irradiation signal after a delay time (T+α) (the time indicated by T+α in FIG. 4), makes the flash light irradiation section irradiate a flash light to a droplet, and repeats the same control, so that an image that looks as if the same droplet 200 is photographed by a high-speed camera and is moving (flying) sequentially can be obtained.
Furthermore, Patent Document 3 discloses an image capturing method in which a light source emits a light every time a signal is sent to irradiate a diesel spray, and the light emission start time from the injection is extended every injection by the delay time interval, so when the observation or the image-capturing is performed in a dark room, the spray 4 can be observed as if it is slowly developing.